User Profile

ictc · 2026-08-17T09:04:14+00:00

Captured the SPMI line on the oscilloscope (1V/div @ 50us/div):

There IS a clear 1.8V data/clock burst from the T2 right at power-on.

This confirms the T2 is executing its initial sequence and sending the SPMI command to U7800. However, U7800 still fails to output/sustain PP3V3_S5.

Since T2 communication is verified present, what hardware condition, PWR_GOOD, or internal PMIC trigger line should I trace next on U7800 that could prevent it from executing the S5 turn-on request?...

ictc · 08-13-2026, 11:31 AM

PMU_SYS_ALIVE is present without battery connected

1. Power Rails / PMIC Status:
- PMU_SYS_ALIVE = 1.78V (measured on bench without battery) -> U7800 internal logic is alive.
- PP1V8_AWAKE = 1.8V -> Present.
- PP3V3_AWAKE = 3.3V -> Present.
- PP1V1_SLPS2R & PP0V8_SLPS2R -> Both present and within spec.
- PP2V5_NAND_SSD1 = 2.5V -> Present and stable (U9580 cleaned and fully operational despite mild external liquid corrosion, no high-side short to PPBUS).

2. The Issue:
- PP3V3_S5 = 0V (Diode mode...

ictc · 08-13-2026, 08:21 AM

2.5v SSD it's OK

ictc · 08-12-2026, 12:46 AM

Small correction to previous findings and new progress made:
Power Delivery: All 4 USB-C ports do in fact reach 20V even without the battery connected. UPC_PMU_RESET is present at 1.8V (with battery/charger connected).

Awake / Primary Rails:
PPBUS_G3H = 12.6V
PPVDDCPU_AWAKE = 0.754V
PP1V8_SLPS2R = 1.8V
PP1V8_AWAKE = 1.8V (present when battery is connected)
PP3V3_G3H_RTC = 3.39V at U7800

Missing Power Rail: PP3V3_S5 is missing (0V).
Measurements: Diode mode on PP3V3_S5 measures ~0.30V, so there is no short to...

ictc · 08-03-2026, 11:31 PM

Hi everyone, I wanted to update the thread with the final resolution to help anyone facing a similar power fault. The laptop is now fully repaired and working!

Root Cause & Fault Analysis:
The issue originated from a short on the SMBus communication line between the Charging IC and the Super I/O:
The TVS ESD protection diode on the SMBus line shorted to ground.
The fault damaged the logic interfaces on the connected ICs, resulting in hard shorts to ground on the SMBus pins of both the Charging IC and the Super I/O (ITE IT5125VG).

Repair...

ictc · 07-14-2026, 10:43 AM

Thank you all!

Just an update for completeness.

I eventually traced the fault back to the EC after the customer accidentally shorted the battery connector while attempting to upgrade the RAM. This caused a short on the P_SMB0_DAT line, which is connected mainly to two key components on the motherboard:

the BQ24800 charging IC
the ITE Super I/O (EC)

Both devices showed a dead short on the pin connected to the P_SMB0_DAT line.

After removing both ICs, along with the TVS diode (which had failed open), the short disappeared completely. This makes me...

ictc · 07-14-2026, 12:51 AM

Hi Sparo and reformatt , Thank you so much for the quick, extremely helpful, and detailed answers!
@Sparo: That is fantastic news about the auto-programming feature on this platform. It saves a lot of headaches. Also, thank you for the link to the EC file and for offering to extract it from my BIOS dump, I really appreciate your availability. Since I have a backup of my original BIOS dump, I might try to extract the 192KB EC partition myself first to learn the process, but having your file as a benchmark is a lifesaver.
@reformatt: You hit the nail on the head. That AliExpress...

ictc · 04-21-2026, 10:45 AM

Final Update:

The issue is now RESOLVED. After further investigation, I focused on the PP1V8_S2 rail, injected 1,8V and spotted the infamous badcap ;-)

I found C823A (10uF 0402 capacitor) near U8100 was shorted/leaking. This was causing the PMU to detect an over-current condition as soon as it attempted to enable the S2 state, leading to the infinite 0.12A reset loop.

Solution: Replaced C823A on PP1V8_S2. MacBook is now fully functional and booting into macOS.

Thanks for the help!

ictc · 04-20-2026, 09:45 AM

I’ve made some significant progress. I should change the post title at this stage btw... Here is the summary of the work done and the current roadblock:

1. Sensing Circuit Repair (Completed): I found clear evidence of degradation in the voltage sensing section. I have already replaced RD538 and RD539 (PPBUS Voltage Sensor) because they were completely out of spec:

RD538: measured 195kΩ (target 78.7kΩ) replaced with 82kΩ
RD539: measured 59kΩ (target 31.6kΩ) replaced with 33kΩ. Despite restoring these values, the board remained in a loop because PBUS_VSENSE stayed at 0V, as the

...

ictc · 03-17-2026, 02:27 PM

The problem will be to reach the center of the bga with a gel stripper.

ictc · 03-17-2026, 02:15 PM

By the way having the related schematic and boardview available on the forum would also be really useful.

ictc · 03-17-2026, 02:11 PM

Thank you very much. I didn’t want to bother anyone, so I managed to trace the resistor path with a multimeter and compare it with a similar schematic to determine the missing value. Fortunately, many Lenovo boards share very similar layouts and component naming. It turned out to be a 1 MΩ resistor. I hope that was the one preventing the board from powering up properly. I’ll verify it tomorrow when I’m back at the bench....

ictc · 03-17-2026, 10:26 AM

Thanks for your reply, I understand the rules about paid resources.

I’ve posted a specific request for identifying a component as well. I noticed you shared here a small boardview snippet that allready helped me a lot in identifing the first resistor, so I was wondering if you could do the same just to help pinpoint the other one.

If not, I’ll try to find the boardview myself. Thanks anyway.

User Profile

Profile Sidebar

Leave a comment:

Leave a comment:

820-01827 (A1990) - PM_RSMRST_L stays LOW, Revive halts at 66% (60mA stall)

Schematic and Board View for MS-15431 VER 2.0

Leave a comment:

Leave a comment:

Leave a comment:

ASUS FX516PC - IT5125VG-192 - Does this EC support auto-programming?

MacBook Pro 13” 2020 (A2251) WindowServer WATCHDOG crash on wake unless external monitor is connected.

Leave a comment:

Leave a comment:

MacBook Air M1 (820-02016) Stuck at 5V - Power Cycle Loop 0.04A to 0.12A - No Shorts Found

ADVANTECH RSB-4760 RISC 3.5" single board computer not booting up

Leave a comment:

Leave a comment:

identification of a resistor value on NM-F701